The present invention relates to improvements in zoom lenses and it relates more particularly to an improved zoom lens which may operate as an objective lens system for macro-photography of the type, in which an objective lens system includes at least two movable components which are movable so as to effect selective magnification. In this lens system, the focusing for macro-photography is effected by adjusting the position of one component relative to another into a position different from that taken upon zooming, with the order of arrangement of the aforesaid movable components within the system being maintained unchanged, or by moving the lens components which have been maintained stationary during zooming.
A zoom lens system having a macro-photographing mechanism of the type described above is known, such as in the Japanese Patent Publication No. SHO50-28829, in which a single operating ring is moved along the optical axis relative to a fixed lens barrel, either upon zooming or upon focusing for macro-photography.
The prior art zoom lens barrel has the following shortcomings:
(1) Fine adjustment is difficult in focusing for macro-photography.
(2) Because of a single operation, discrimination between the macro-focusing operation and the zooming operation is difficult, thus presenting the possibility of a faulty operation.
(3) Machining of the cam ring is difficult and the construction of the lens barrel is complex, so that its cost is increased and its reliability is reduced.
(4) Rapid switching from a zooming operation to a macro-focusing operation and vice-versa is difficult to achieve.